Tectonic units in the Pennsylvania-Delaware Piedmont : evidence from regional metamorphism and structure / James Edward Alcock.

Format:

Book

Manuscript

Microformat

Thesis/Dissertation

Author/Creator:

Alcock, J. (James Edward)

Contributor:

Wagner, Mary Emma, advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Penn dissertations--Geology.

Geology--Penn dissertations.

Local Subjects:

Penn dissertations--Geology.

Geology--Penn dissertations.

Physical Description:

viii, 259 leaves : illustrations; 29 cm

Production:

1989.

Summary:

The Pennsylvania-Delaware Piedmont is thought to have been deformed and metamorphosed in the Early Paleozoic during the collision of lithospheric plates. Previous work has identified two tectonic units in the region, rocks from the pre-Taconic North American continental margin (from the subducted plate) and the infrastructure of the magmatic arc (the Wilmington Complex). An analysis of metamorphism and structure presented in this thesis identifies the Wissahickon Formation and associated meta-igneous rocks as a third.

Detailed mapping in southern Chester County, PA has found discordant structural relations at the contact of the Wissahickon (including associated meta-igneous rocks) with the Cockeysville Marble, Setters Formation, and Baltimore Gneiss. The structural discontinuity indicates a thrust emplacement of the Wissahickon that occurred after recumbent folding of the North American margin rocks in the footwall.

South of the Avondale anticline, the contact between the Wissahickon Formation and the Cockeysville Marble is identified as a metamorphic discontinuity. Peak temperature (from mineral assemblages and mineral compositions) is inferred to have been 100-150$\sp\circ$C hotter in the Wissahickon Formation than in the Marble. The distribution of assemblages and mineral textures in the Marble provide evidence for fluid regimes controlled by the addition of water from the Wissahickon. The metamorphic inversion across the contact and the fluid regime in the Marble are consistent with the thrust model.

The metamorphic histories of the different tectonic units are used to propose a tectonic assembly model. First the Wilmington Complex was emplaced above the Wissahickon. After heating and then cooling from peak temperature, the Wissahickon was thrust across the North American margin rocks. It is possible that the thrust that separates the Wissahickon from the North American margin rocks is a boundary between exotic and North American terranes.

Notes:

Supervisor: Mary Emma Wagner.

Thesis (Ph.D. in Geology) -- Graduate School of Arts and Sciences, University of Pennsylvania, 1989.

Includes bibliography.

Local Notes:

University Microfilms order no.:90-06610.

OCLC:

244968449